System writer is missing on WIN2K8 SP2

I have WIN2K8 SP2 with oracle 10g and I am using CA ARC backup to take backup. From last few days system stage backup failed and reason is “Failed to create system state shado copy” I think it use VSS service to take shadow copy. Volume shadow copy service is running on target server. But when I run vssadmin list writers there is no systemwriter listed. I think this is the reason of this problem. Anyone have any advice how could I bring back the systemwriter.